To evaluate change of serum $beta_2-microglobulin$ concentration$(seta_2-MG)$ and the usefulness of $seta_2-MG$ and $seta_2-MG/serum$ creatinine concentration(sCr) ratio in various renal diseases, $seta_2-MG$ and sCr were measured in 25 normal controls and 90 patients of various renal diseases(16 cases of glomerulonephritis, 12 cases of acute renal failure, 8 cases of chronic renal failure, 24 cases of nephrotic syndrome, 15 cases of tubulointerstitial diseases and 15 cases of lupus nephritis) using $Phadebas^circledR$ $Beta_2-Micro$ Test kits. The results were as follows; 1) In normal control, the mean value of $seta_2-MG$ was $1.65{pm}0.41mg/l$ and the mean value of $seta_2-MG/sCr$ ratio was $0.14{pm}0.05$. 2) In various renal diseases, the mean value of $seta_2-MG$ was $6.74{pm}5.47mg/l$. The mean value of $seta_2-MG/sCr$ ratio was $0.24{pm}0.11$ and significantly elevated than that of normal control. (p<0.05) 3) The correlation between $seta_2-MG$ and sCr in glomerular and tubulointerstitial disease was log $seta_2-MG-0.90$ log sCr-0.48 and its correlation coefficient was 0.78(p<0.05). 4) In glomerular disease, the correlation between $seta_2-MG$ and sCr was log $seta_2-MG-0.89$ log sCr-0.46(r - 0.76) and in tubulointerstitial disease, it was log, $seta2-MG-0.95$ log sCr-0.59 (r-0.87). There was no significant difference between the two groups(p<0.05). 5) Among 32 cases of glomerular and tubulointerstitial disease patients, whose sCr was within normal range, 17 cases showed elevated $seta_2-MG$. The mean values of $seta_2-MG/sCr$ ratio in these patients was $0.30{pm}0.14$ and significantly elevated than that of normal control(p<0.05). 6) In 15 cases of lupus nephritis, 12 cases showed elevated $seta_2-MG$ with normal sCr and 12 cases showed elevated $seta_2-MG/sCr$ ratio. With above results, it was found that the $seta_2MG$ can be used as an index of glomerular filtration rate as in the case of sCr and that $seta_2-MG/sCr$ ratio can be used as a tool in early detection of slightly decreased glomerular filtration rate and in detection of the renal disease of increased $eta_2-MG$ production.